Knowledge Bank

The time dependence of the rotational correlation function of the vibrational transition moment of the $\nu 4$ fundamental of $CH2Cl2(283cm-1)$ between 0 and $1.6\times 10-12$ sec. has been obtained by the Fourier-inversion of the absorption band about the band center (R. G. Gordon, J. Chem. Phys. 43, 1307(1965) for the pure liquid and for $CH2Cl2$-polystyrene solutions of varying concentrations (molar ratio of $C6H5-CH-CH2/CH2Cl2$ of 0 to 1.5). The decay of the rotational motion of the direction of the transition moment, that is the direction of the $C2$-symmetry axis of the molecule, to Brownian motion is exponential (Markov process) after an initial period of relatively free rotation during the first $0.1-0.2\times 10-12$ sec. and has dropped to l/e of its initial value after $\sim 0.8\times 10-12$ sec. The rate of decay is little influenced by the presence of the polymer; this indicates that the component of the rotational diffusion-constant tensor is about the same in the different environments.